IBS can be caused by all sort of things, not just the meds. In your case, the long list of pills seems like the obvious culprit. I’ve been bloated since the vas and have all the symptoms you’ve described. They were worst immediately following the surgery and I never once took any medication. I remember two weeks after the vas I had a slice of pizza for lunch and my stomach gargled for an hour straight every time I moved. It was loud enough even my patient said something about it.
I didn’t know it at the time but IBS is common in fibromyalgia, which I was recently diagnosed with. It’s also linked to multiple neurodegenerative disorders. I spoke to a patient who happens to be head of the GI department at the university. His comment was we are either too stupid or too arrogant to think we understand what causes IBS. His view was it’s a nervous system issue and he isn’t convinced a pill is going to help it.